1. Field of the Invention
The present invention relates to agricultural implements, and, more specifically, to castor wheel assemblies used in such implements.
2. Description of the Related Art
One of the widely used support systems for allowing ground movement at a precise elevation above the ground utilizes trailing wheels and front castor wheels. Towed tillage implements advantageously use this type of support system to more closely follow the ground contours. The trailing wheels (and the front castor wheels) are usually movable up and down so that the height of the implement frame above the ground may be controlled. Along with the trailing wheels, which have a fixed axis of rotation, there are usually a pair of forward castor wheels, widely used, so that the towed direction of the implement is followed by pivoting of the castor wheels. In addition to the field position, the rear wheels and the front castor wheels may be placed in a transport position in which the ground engaging elements of the tillage implement are elevated above the surface level of the soil.
While the castor wheels allow a simplified way of following the direction of movement set by a tractor pulling the implement, they do experience, under operating conditions, an oscillation that is considered to be wobbling. A number of factors can contribute to the wobble and they include weight balance, internal friction, towing speed and trailing arm geometry.
Because many of these factors are dynamic and not controlled necessarily by the machine operator, it has been proposed to include friction elements in the pivoting support for the castor wheel so as to inhibit wobbling. The friction elements, at first glance, offer a direct solution to the problem. However, the wear incurred by friction elements over time, decreases the inhibiting force and results in less effective damping of the wobble. It has been proposed to use spring loaded brake elements to offer a consistent friction force to inhibit the wobbling over an extended period of time. However, this approach introduces additional cost and complexity. Furthermore, the friction mechanisms maybe prone to accumulation of soil and other debris to diminish their effectiveness.
Accordingly, what is needed in the art is a simplified way to introduce friction in a castor wheel assembly.